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The Infamous Giant Hogweed

The Infamous Giant Hogweed

www.btny.purdue.edu/weedscience/

Glenn Nice WS-32-W Bill Johnson The Infamous Giant Hogweed Tom Bauman I sent out a “heads up” message not too long ago about the reported sighting of giant Purdue Extension Weed Science hogweed ( mantegazzianum) near Warsaw, Indiana. Although I had heard about this weed, I had not given it much attention before. Giant hogweed has some fame in some parts of the world. The British rock group Genesis even wrote a song about it.

Identification:

As its name suggests, the first thing you may notice about giant hogweed is its stature. When it flowers, the can reach a height of 10 to 15 ft (3 to 5 m; Figure 1.). The stems are hollow, 2 to 4 inches (5 to 10 cm) in diameter, with dark reddish-purple spots and bristles (Figure 2). The compound are deeply incised and in some cases can grow to a scary width of 5 ft (1.5 m; Figures 3 and 4). Being in the carrot family, giant hogweed has a characteristic floral arrangement. This umbel can be as large as 2.5 ft (76 cm) wide (Figure 5).

Giant hogweed resembles the native cow (); however, cow parsnip is smaller (Table 1). Also, cow parsnip appears very hairy under the , whereas the undersides of giant hogweed leaves have fine, short hairs (1). Giant hogweed stems have reddish-purple spots on them, whereas cow parsnip stems generally do not.

Giant hogweed can live in a variety of areas. It might be found in areas of uncultivated waste land and vacant lots, or along railroads, roads, creeks, and streams. It often grows in wet areas.

Invasive Nature and Toxicity:

Giant hogweed is a perennial and a member of the carrot family, . Giant hogweed is on the Federal Noxious Weed List, partially due to its aggressive, invasive nature. It spreads through tuberous root stalks and forms a solid canopy that chokes out Figure 1. Giant hogweed many native . More important is the possible impact on human health. This plant should be avoided like you would avoid poison ivy. Giant hogweed produces a clear, watery sap that can cause “photo-dermatitis,” which is sensitivity to sunlight (ultraviolet radiation). Photo-dermititis can result in swelling, severe blistering, and painful dermatitis, so avoid contact with exposed skin.

One case of giant hogweed poisoning occurred in the 1970s in Great Britain, where children contracted photo-dermatitis by playing with giant hogweed stems (2). If you come in contact with giant hogweed, wash with soap and water immediately. If you should happen to see this plant, contact your local county educator or Cloyce Hedge ([email protected]) at the Department of Natural Resources. The Infamous Giant Hogweed Oct 25, 2004 (revised)

Control: Non-chemical Digging up the plants appears to be the most effective non-chemical control method. Wear protective clothing when working around giant hogweed so the sap does not touch your skin. www.btny.purdue.edu/weedscience/ Cut plants below ground level. Try to remove the tap roots, for these can sprout new shoots. Digging up giant hogweed requires repeated efforts and monitoring for regrowth. It will be difficult to remove all the tuberous root stocks. Mowing, however, may result in increased growth of giant hogweed. Repeated mowing could wear plants down by starving the roots, but vigilance and determination would be required. Grazing and trampling by animals tolerant to giant hogweed toxins, such as cattle and sheep, can also wear the plants down; however, one brochure on this plant states that this would not control the plants (3).

Chemical Glyphosate or triclopyr appear to be the best way to control giant hogweed chemically. Repeated applications may be necessary. Several home-use glyphosate products can be purchased in local garden centers. Commercial glyphosate products can also be used, but if you don’t have the proper equipment or training to apply such products, seek help from an experienced applicator. If glyphosate spray comes in contact with desirable plants, they can be injured. So apply glyphosate carefully. Control is most effective when plants are less than five feet tall and before they flower. If the plant has flowered, removing the flowers prevents it from producing seed.

Background:

Originally from Asia, giant hogweed can now be found around the world, including Australia, several European countries, the U.S. and Canada (2, 4). Researchers suspect giant hogweed Figure 2. Giant hogweed stem, look for made its way into these countries as an ornamental. Its size makes it somewhat of an oddity the reddish-purple spots. and probably was imported by gardeners who wanted something unique. As reported on the USDA plant database (http://plants.usda.gov) giant hogweed is in Maine, Michigan, , Pennsylvania, and Washington. Fruit from this group of plants is often used as a spice in Iranian cooking and is mentioned in the Federal Noxious Weed Inspection Guide (2). Occasionally inspectors have found lots of seed from Heracleum species imported for ethnic food stores (2).

Figure 3. Giant hogweed leaf. Figure 4. Giant hogweed growing in a parking lot. The Infamous Giant Hogweed Oct 25, 2004 (revised)

Table 1. Comparison of giant hogweed and cow parsnip. www.btny.purdue.edu/weedscience/

Giant Hogweed Cow Parsnip Information listed here is based on Height 10 to 15 feet 4 to 8 feet research and outreach extension programming at Purdue University Stem Hollow, 2 to 4 inches in Hollow, often 2 inches in and elsewhere. diameter, dark reddish purple diameter at base, no spots The use of trade names is for clarity to readers of this site, spots does not imply endorsement of a particular brand nor does exclusion Leaves Compound leaves deeply Compound leaves deeply imply non-approval. Always consult incised, up to 5 feet wide, incised, up to almost 1 the herbicide label for the most short hairs beneath leaf foot wide, very pubescent current and update precautions beneath and restrictions. Copies, reproductions, or transcriptions of this document or its information Flower Umbel up to 2.5 feet wide Unbel 6 to 12 inches wide must bear the statement ‘Produced and prepared by Purdue University Extension Weed Sources: Science’ unless approval is given by the author. 1) N. Britton and A. Brown. 1913 (reprinted 1970). An illustrated Flora of the Northern and Canada Vol 2 p 635. 2) Westbrooks, R.G. (Accessed 6/30/04) Sommier & Levier. FEDERAL NOXIOUS WEED INSPECTION GUIDE. Whiteville Plant Methods Center, Whiteville, NC. (http://www.ceris.purdue.edu/napis/pests/ghw/facts.txt) 3) Anonymous. (Accessed 7/1/04) Homeowners Guide to Managing Giant Hogweed. Vermont agency of Agriculture and Food Markets. (http://www.uvm.edu/mastergardener/pdf%20files/giant_hogweed_ homeowners_brochure__Read-Only_.pdf) 4) Anonymous. (Accessed 6/30/04) Non-Native Fresh Water Plants Giant Hogweed. Washington Department of Ecology. (http://www.ecy. wa.gov/programs/wq/plants/weeds/aqua012.html) 5) Anonymous. (Accessed 6/30/04) Giant Hogweed. King County, Natural Resources and Parks. (http://dnr.metrokc.gov/wlr/LANDS/ weeds/hogweed.htm) Figure 5. Giant hogweed inflorescence

Picture Source: Surry and Berks, 1977 and 2001, respectively. As seen on the BioImage: The Virtual Field-Guide (UK) web site; (http://www.bioimages.org.uk/HTML/T10402.HTM)

PURDUE EXTENSION 10/04

It is the policy of the Purdue University Cooperative Extension Service, David C. Petritz, Director, that all persons shall have equal opportunity and access to the programs and facilities without regard to race, color, sex, religion, national origin, age, marital status, parental status, sexual orientation, or disability. Purdue University is an Affirmative Action institution. This material may be available in alternative formats. 1-888-EXT-INFO http://www.ces.purdue.edu/new

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